Just Another Day in Worldly N.Y. : Pageantry: City residents take an awesome assemblage of power perfectly in stride.

UNITED NATIONS — The largest gathering of world leaders in history converged Sunday on the United Nations for a 50th birthday bash of King Kong proportions, a show that would have closed down almost any other city in the world.

Here in the Big Apple, though, with not an empty bed among the city's 59,000 hotel rooms and security tighter than the glove in the O.J. Simpson trial, New Yorkers yawned and carried on, picking their way with uncharacteristic good grace around motorcade routes reserved for limousines and demonstrations by fasting Tibetans, chanting Tamils and rebellious Zairians. So who ever heard of Brig. Gen. Teodoro Mbasogo of Equatorial Guinea, anyway?

"Hey, pal, this is New Yaawk," cabbie Stanley Horowitz said. "No big deal. We get celebrities here all the time."

Perhaps. But this choreographed affair was an awesome spectacle--the membership of the world's most exclusive and powerful club sitting together in one room, more than 180 kings and presidents, prime ministers and generals, dictators and tyrants who, by election, heredity or the exercise of force, had come to power and now hold in their hands the welfare of billions of people.

They started arriving one by one shortly after 7 a.m., coming down 1st Avenue in an armada of limousines to the gleaming U.N. headquarters that was built in the 1950s on a slum tract of slaughterhouses and meatpacking plants along the East River.

Aides scurried to open doors, a gantlet of guards saluted, and U.N. Secretary General Boutros Boutros-Ghali waited on a red carpet. The United Nations' 50th birthday party was about to begin.

"The president of Israel and madame," a protocol officer would announce, slipping in and out of French, English and Spanish. Boutros-Ghali, a former Egyptian foreign minister who is full of old-world charm, greeted each like a long-lost friend--a hug for the Arabs, a handshake for the Westerners, a kissed hand for the women.

Only one person got a chance to give a few orders. That was Paul Shipworth, a Kodak photographer, who admitted that his mouth went dry at the sight of more than 180 leaders and observers standing in front of him for a historic group picture.

"All the way to the middle of the aisle, fill the gap," he said, directing kings and presidents this way and that as if he were moving so many children for a group photo on the last day of summer camp.

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"I've got my favorite president right there looking down," he admonished--and President Clinton obliged, straightening his head.

"I love seeing the ladies; they've got such pretty smiles," he said at another point.

Shipworth held up a picture he had scrawled of a happy face--U.N. protocol had given its OK--and when he got a chorus of chuckles, he started snapping away.

From Sunday to Tuesday, every head of state was scheduled to address the General Assembly, a daunting thought to anyone who knew that it has taken Cuba's Fidel Castro two hours of speechmaking just to warm up or remembered Clinton's keynote address to the 1988 Democratic National Convention.

If every leader merely filled the allotted five minutes, the time consumed would be more than 13 hours. If each went over by just two minutes, five more hours would be added. To keep things on track, a light on the podium turned amber at 4 1/2 minutes and red at five.

Castro, looking quite unrevolutionary in a dark suit and regimental tie, cut himself off right to the second. Clinton speeded through the red light and kept rolling for about an extra five minutes.

"Please, delegates, keep the noise down," an amplified voice requested at one point as leaders, tiring of speeches, chatted and moved around the floor to socialize.

Delegations came and went, fidgeted when the light turned red and applauded politely at the conclusion of each mini-speech.

"I came to you 21 years ago as a fighter for freedom, liberation and independence, carrying with me the torments of my struggling people," Palestine Liberation Organization leader Yasser Arafat said of the day he had addressed the General Assembly wearing an empty holster under his jacket.

"Today, however, I come to you with a heart filled with love and peace, with the olive branch hoisted over the peace of the brave."

In the rows of seats facing Arafat sat a group of leaders as diverse as the countries they ruled and governed: Saudi royalty, wealthy beyond imagination, and the two "regent captains" of San Marino, whose prime industry is the sale of postage stamps; South Africa's Nelson Mandela, winner of the Nobel Peace Prize, and Kenya's Daniel Arap Moi, whose disregard for human rights has drawn worldwide attention; Zaire's Mobutu Sese Seko, who has dipped into his government's treasury for the generation he has held power, and Palau's new president, Kuniwo Nakamura, who put one of his diplomats up in a $60-a-night room outside Manhattan to save his island nation a few dollars.